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Toxicology – Beta-Blocker Toxicity
Source
Beta-blockers include medications such as propranolol, metoprolol, atenolol, nadolol, pindolol, labetalol, and carvedilol. These drugs are commonly used to manage hypertension, cardiac arrhythmias, angina, migraines, and anxiety-related conditions.
Typical Presentation
Toxicity may occur after accidental ingestion (especially in children) or intentional overdose. Patients often present with cardiovascular depression and altered mental status.
Clinical Features
Common findings include bradycardia, hypotension, and varying degrees of heart block. More severe toxicity may lead to ventricular arrhythmias, seizures (especially with propranolol), and central nervous system depression. Additional features can include widened QRS complexes (notably with propranolol), QT prolongation (e.g., with sotalol), and hypoglycemia.
Mechanism of Action
Beta-blockers inhibit β-adrenergic receptors. Blockade of β1 receptors reduces heart rate and contractility, leading to decreased cardiac output. β2 receptor blockade can result in bronchoconstriction. Lipophilic agents, particularly propranolol, cross the blood–brain barrier and can cause central nervous system effects such as sedation, confusion, and seizures.
Management
Treatment is supportive with continuous cardiac monitoring. Interventions may include intravenous fluids, glucagon (to increase intracellular cAMP independent of β-receptors), high-dose insulin therapy with glucose, vasopressors, and cardiac pacing if needed. Sodium bicarbonate may be used for QRS widening, and magnesium for QT prolongation. Lipid emulsion therapy can be considered in severe cases. Bronchodilators are used if bronchospasm develops. Whole bowel irrigation may be indicated for sustained-release ingestions.
Key Points
Source
Beta-blockers include medications such as propranolol, metoprolol, atenolol, nadolol, pindolol, labetalol, and carvedilol. These drugs are commonly used to manage hypertension, cardiac arrhythmias, angina, migraines, and anxiety-related conditions.
Typical Presentation
Toxicity may occur after accidental ingestion (especially in children) or intentional overdose. Patients often present with cardiovascular depression and altered mental status.
Clinical Features
Common findings include bradycardia, hypotension, and varying degrees of heart block. More severe toxicity may lead to ventricular arrhythmias, seizures (especially with propranolol), and central nervous system depression. Additional features can include widened QRS complexes (notably with propranolol), QT prolongation (e.g., with sotalol), and hypoglycemia.
Mechanism of Action
Beta-blockers inhibit β-adrenergic receptors. Blockade of β1 receptors reduces heart rate and contractility, leading to decreased cardiac output. β2 receptor blockade can result in bronchoconstriction. Lipophilic agents, particularly propranolol, cross the blood–brain barrier and can cause central nervous system effects such as sedation, confusion, and seizures.
Management
Treatment is supportive with continuous cardiac monitoring. Interventions may include intravenous fluids, glucagon (to increase intracellular cAMP independent of β-receptors), high-dose insulin therapy with glucose, vasopressors, and cardiac pacing if needed. Sodium bicarbonate may be used for QRS widening, and magnesium for QT prolongation. Lipid emulsion therapy can be considered in severe cases. Bronchodilators are used if bronchospasm develops. Whole bowel irrigation may be indicated for sustained-release ingestions.
Key Points
- Lipophilic beta-blockers can cause early and significant central nervous system depression.
- Hypoglycemia is more commonly seen compared to calcium channel blocker toxicity.
- Bronchospasm may occur, particularly in patients with underlying respiratory disease.
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